Method for making electrically conductive vitreous materials



United States Patent 3,342,753 METHOD FOR MAKING ELECTRICALLY CONDUCTIVE VITREOUS MATERIALS Hendrikus Johan Lodewijk Trap, Emmasingel, Eindhoven,

Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 21, 1963, Ser. No. 266,791 Claims priority, application Netherlands, Mar. 30, 1962, 276,626 Claims. (Cl. 252518) My invention relates to vitreous materials exhibiting electrical conductivity and to a method of manufacturing these materials.

Sintered oxidic materials which exhibit electrical conductivity due to the material containing at least one metal ion in more than one valency are known. The possibilities for the use of such material-s are somewhat limited, since they are manufactured by sintering and hence, in the most favorable case products are obtained which approach, but never attain the theoretical density, Consequently, such products do not have optimum properties.

The shaping of sintered bodies is also subject to certain restrictions; and, the sintering treatment usually requires a high temperature. Consequently, such bodies are not particularly attractive either from a technological view point, or with a view to the reproducibility of the desired physical properties. For these two reasons, preference should be given to electrically conductive vitreous materials. However, an electrically-conductive glass having a conductivity sufficiently high for practical use has not been described heretofore.

A known electrically conductive glass consists of an alkali-silicate glass containing titanium oxide in which the titanium ions are present in different valencies and in a total quantity of 14 to 45% by weight, calculated as the oxide. In the most favorable case such a glass has a specific resistance of not less than 20,000 ohms-cm, measured at 50 C. (cf. Table 11).

Accordingly, it is a principal object of my invention to provide an electrically conductive glass of low specific resistance and a high electrical conductivity.

A further object of my invention is to provide an electrically conductive glass having a specific resistance of only to 1,000 ohms-cm, measured at 50 C.

A still further object of my invention is to provide a method of making an electrically conductive glass.

These and further objects of the invention will appear as the specification progresses.

In accordance with the invention, an electrically conductive glass having a specific resistance measured at 50 C., of only 10 to 1,000 ohms-cm. has a composition constituted by at least 80 mol. percent of the following components: (1) At least one of the oxides SiO and E 0 and further A1 0 (2) Na 0 and the oxides Fe O and FeO in a molecular ratio between 1:2 and 4:1, in quantities in mol. percent defined in the following manner, the total of Fe O and FeO being calculated as F5304:

SiO +B O 75 302[B O SiO 65- A [B 0 21-- /6[SlO2+B O F6 O 40% [SiO +B O 2 Al O 30% [SiO 3 Na O 30 while the remaining maximum portion of mol. percent one or more of the following components may be present:

Mol. percent In order to obtain glass of this composition,,the oxides, or compounds which change to these oxides upon heating, are melted in the manner usual in the glass industry in a weakly-reducing to a weakly-oxidizing atmosphere at a temperature from 1,000 C. to 1,650 C.

A weakly-reducing atmosphere is obtained by melting the initial materials in a flame which is supplied with. a mixture of hydrogen and oxygen containing an excess of 10% by volume of hydrogen with respect to the stoichiometric quantity by volume of oxy-hydrogen gas. A weakly-oxidizing atmosphere is obtained within a flame which is supplied by light gas and a small excess of oxygen, for example, in a quantity of 10% by volume.

The presence of ferric-ions in addition to ferrous-ions in a ratio which lies between 1:1 and 8:1, dependent upon which of the aforementioned kinds of atmosphere is chosen in which the glass is melted, is essential to the high electrical conductivity of glasses in accordance with the invention. For manufacturing the glass, the ironoxide may be added to the mixture in the form of magnetite (Fe O ),-if desired together with a ferrous-compound, for example, ferrous oxalate. If added in the form of separate ferric and ferrous compounds, for example, in the form of Fe O and ferrous oxalate, a deviation is found which lies within the tolerance limit. So if Fe O is used as the initial material, a reaction takes place between the Fe O and the remaining components of the glass mixture. A comparison of the two methods of adding the iron-oxide by plotting on a graph log p, measured for example at C., of a number of compositions in which iron oxide has been added to the mixture in the form of Fe O and log of the same composiitons in which the oxide has been added in the form of a mixture of Fe O and ferrous oxalate, gives a number of points which, on correction of the log -values exhibit a straight-line relationship log p'=0.958 log p0.005 upon correction of log a straight-line relationship log p' =0.45 log p-I-1.41

is found. From this also appears the chemical reaction between the ferric oxide and the remaining components of the mixture and, furthermore, that the addition of iron oxide in the form of separate ferric and ferrous compounds is to be preferred.

It should also be noted that in glasses which do not contain cobalt oxide in trivalent and bivalent form, the melting atmosphere is only slightly critical with regard to the value obtained for the specific resistance. If, on the contrary, it is critical, melting in a weakly-reducing atmosphere yields log p-values lower by approximately unity than the values obtained upon melting in a weakly-oxidizing atmosphere. The conductivity of the glasses may be influenced by adding cobalt ions.

'stivity measureits. The resislog P the value of B being obtained from re ments at 50 C., 100 C., 150 C., 200 0., 300 C. and 500 C. The value of E in electron volts results from multiplication of B by the factor 0.l98 l0- Table II shows, for purposes of comparison, the same physical properties of some titanium-containing electrically-conductive glasses. Although it has been indicated elsewhere that such glasses have resistivities of from 2 to 200 ohmscm., the temperature at which such values were obtained is not specified. Further investigation of those compositions having the lowest specified resistivity values and with measurements performed at 50 C. and 100 C. indicate the results are considerably less favorable than those of compositions in accordance with the invention.

Finally, Table III represents some compositions which contain the components in accordance with the invention, in quantities lying outside the specified lim tivities of bodies of such compositions are considerably higher than those in accordance with the invention.

TABLE I ters,

ction ing iger coun in conne s logarithm of -cm. obtained but have a pitchinally, the activat calculated from the oves to a considerable exin particular its hardness and 50 C. The reference signate the melting atmospheres g atmosphere and the reducing ion of the glass, dependent upon the thermal g out as small crystals in finely dis- This does not substantially influence the conmeasured at 100 0X and red de Glasses in accordance with the invention are usable for example, toasters, as bulbs for Ge These glasses can be crystallized in known manner, a

The invention will be described further Table I shows a la-r e number of compositions in ac- 611686 36 07982 998 5 5 557075Mw 3270 0 A V 00000000000001%0M%0%%WNWWMHN% A E MW 000 00QQQQQQQQQQQQQQQQQQQQQQQQ E aw i 94 U .1483 307 2 3 C G 7 6 0397M814 9m0 U -UQ$$0M U m o R 22 H .11120L2ZZ3 .QWZQMLZO .2 R 0 e 5 m P P I 3 569 82 1 W X IM44ZM55HMMQN %M% m m "QWNM "m n n n n n n M "we W x v l O 33333222222311122 n n 0123 m "3 n W H n n "2 "0 1 O .nw 77 n C e n mM wflww "m n M a R 22 .3 "3110 .2 u a R m 0 1 m W K n 9923104302 014415 n 2709 0 .8 g X l O .22333222222311122 n n 0122 m m m m m m m m m m2 m0 1m 0 2 m n 0 F S n n a C 0 n u n u u n O u n u u n 5 mw n n m n n n g N u u M n U n u 5 5 0 85865001 w n Z 54 33198760504544 C u I I O 57 2552 5 n E O u n n 73 6221 876753075 L a N .3 &B2 2 LL100 7 &2 22LL H B B U A m T m 0 .58 3553 5 n u n u u u n n 0 n u n u 6 H n n g n 73 6221 875353075 n H H n .B l m M 111002222211 u n u u u n n W F c r. e m p O 4 6862 48 n 08 t m m m aaaa nsaa 5 &3 m a n h I m B 0 w PM A. a a v I a m w ......I..I8262II .II I w o p O .1 .1 2 O 11 .1 t l m m A O 0 C 4 5 5 D. 3 O 131411064246 246 84 6 7 5 m 0 3 0 4408642086401080864236943 3 v F 1121111211112121.1ll32ll3wnw h3mnmm%w b bfimmmflfi C W. nw 5 5 5 5 2820161284820482 08 0 6 no 0 a SOfiomlSJU N 1222211%%2B1%%2%2BM1 H 1 MMH%MB%N% T 3 5 5 5 5 5 2 O 57 2557 25-0359025 6 on 1 m 50 2 44. a 467665476654227665482623062 0 M 22112211EZMWHB T 3 2 1 3 0. III. w 0003 00 B 3% n n n n n n S 444343 5 5 5 5 3 3 .1 204073040730 3 050403 S 343445634456 N 111111 as conducting seals, glass electrodes, as heating elements of,

and the like. They are not transparent black color.

varying port treatment, separatin persed form ductivity of the glass, but impr tent its mechanical properties,

and its breakage-strength.

with the following examples which are illustrative thereof, the invention itself being defined in the following claims. 15

cordance with the invention, and the Brigg the value of the specific resistance p in ohm therewith,

symbols used, viz. the oxidizin atmosphere in the aforesaid sense, F

energy E in electron volts is given,

value of B of the relation TABLE III Composition in mol. percent log p 100 0. log p 50 0. EA

SiOz B203 A1203 NazO F8304 C0304 MnO MgO NiO ZnO CaO SrO Ox. Red. x. Red. (e.V.)

While I have described my invention with reference to specific examples and applications, other modifications will be apparent to those skilled in this art without departing from the spirit and scope of the invention.

What I claim is:

1. A method of manufacturing an electrically conductive vitreous material comprising the steps, mixing A1 0 Na O, iron oxide in the form of Fe O at least one oxide selected from the group consisting of SiO and E 0 said oxides together constituting a first group of oxides, and an oxide of the group consisting of C0 0 MnO, NiO, ZnO, MgO, C210, and SrO in proportions yielding upon heating a composition constituted of at least 80 mol percent of the first group of oxides in the following proportions:

15 SiO +B O 75 302[B O SiO 65-% [B 0 2 Al O 30% [SiO 3 Na O 30 and not more than mol percent of the second group of oxides in the following proportions:

M01 percent and heating said mixture to a temperature of about 1000 C. to 1650 C. in a weakly-reducing to weakly-oxidizing atmosphere to melt said constituents and form said vitreous material.

2. A method as claimed in claim 1 in which the atmosphere is constituted of combustion products of a mixture of oxygen and hydrogen containing an excess of 10% by volume of hydrogen with respect to the stoichiometric quantity by volume of oxyhydrogen gas.

3. A method as claimed in claim 1 in which the atmosphere is constituted of combustion products of a mixture of light gas and about 10% by volume of oxygen.

consisting of C0 0 MnO, NiO, ZnO, MgO, CaO, and

SrO in proportions yielding upon heating a composition constituted of at least 80 mol percent of the first group of oxides in the following proportions:

15 SiO +B O 75 30 2 B O SiO B 0 2 Al O 30% [SiO 3 Na O 30 and not more than 20 mol percent of the second group of oxides in the following proportions:

Mol percent C0304 MnO 12 NiO 8 ZnO 12 MgO 8 CaO 6 SrO 6 and heating said mixture to a temperature of about 1000 C. to 1650 C. in a weakly-reducing to weakly-oxidizing atmosphere to melt said constituents and form said vitreous material.

References Cited UNITED STATES PATENTS 2,616,859 11/1952 Verwey 252-520 2,786,819 3/1957 Smith et al. 252.519 3,093,598 6/1963 McMillan et al. 252518 X LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

I. D. WELSH, Assistant Examiner. 

1. A METHOD OF MANUFACTURING AN ELECTRICALLY CONDUCTIVE VITREOUS MATERIAL COMPRISING THE STEPS, MIXING AL2O3, NA2O, IRON OXIDE IN THE FORM OF FE3O4, AT LEAST ONE OXIDE SELECTED FROM THE GROUP CONSISTING OF SIO2 AND B2O3, SAID OXIDES TOGETHER CONSTITUTING A FIRST GROUP OF OXIDES, AND AN OXIDE OF THE GROUP CONSISTING OF CO3O4, MNO, NIO, ANO, MGO, CAO, AND SRO IN PROPORTIONS YIELDING UPON HEATING A COMPOSITION CONSTITUTED OF AT LEAST 80 MOL PERCENT OF THE FIRST GROUP OF OXIDES IN THE FOLLOWING PROPORTIONS: 15<SIOI+B2O3<75 30-2(B2O3)$SIO2$65-3/4(BIO3) 21-1/6(SIO2+B2O3)<FE3O4<40-1/3(SIO2+B2O3) 2<AL2O3<30-3/8(SIO2) 3<NAI3<30 AND NOT MORE THAN 20 MOL PERCENT OF THE SECOND GROUP OF OXIDES IN THE FOLLOWING PROPORTIONS: SP% MOL PERCENT CO3O4 <12 MNO <12 NIO <8 ZNO <12 MGO <8 CAO <6 SRO <6SP@ AND HEATING SAID MIXTURE TO A TEMPERATURE OF ABOUT 1000* C. TO 1650*C. IN A WEAKLY-REDUCING TO WEAKLY-OXIDIZING ATMOSPHERE TO MELT SAID CONSTITUENTS AND FORM SAID VITREOUS MATERIAL. 